This invention relates to an optical PCM (pulse code modulation) transmission system, and more particularly to, a binary optical transmission system for optical data link, such as multi-channel optical link where multiple light-emitting elements are integrated, optical wireless transmission and plastic-fiber optical link.
FIG. 1 shows the composition of a conventional optical data link using PCM transmission system. In the conventional optical data link in FIG. 1, an encoding circuit 10 conducts the encoding that, by scramble or block-coding, the ratio of bit number of luminous parts and bit number of non-luminous parts in a certain time section is made 1:1. For example, in 8B10B encoding method used in Fibre Channel etc., as shown in FIG. 2, when encoding 8-bit binary data sequence (256 kinds) into 10-bit binary data sequence (1024 kinds), combinations that both logic xe2x80x981xe2x80x99 and logic xe2x80x980xe2x80x99 are of five bits, combinations that logic xe2x80x981xe2x80x99 and logic xe2x80x980xe2x80x99 are of four bits and six bits, respectively, and combinations that logic xe2x80x981xe2x80x99 and logic xe2x80x980xe2x80x99 are of six bits and four bits, respectively, are applied as data sequences after encoding so, the optical transmission is conducted using this applied encoding. The other combinations are not used for the optical transmission.
Also, in FIG. 1, an amplifier 5 and a binary quantization circuit 6 are AC-coupled using capacitor 42, and a RC integrator 44 to cancel the internal offset of the binary quantization circuit 6 is added. With such a composition, a simple optical reception front-end circuit 30A can be applied.
However, in optical data links, the output power of transmit light is restricted by safety and the lifetime and consumed power of light-emitting element, and the minimum level of receive light is restricted not only by the internal noise of receiver but also by the interference of extraneous white light or electrical crosstalk. In multi-channel optical link, optical wireless transmission and plastic-fiber optical link, a light source with 850 [nm] or 650 [nm] band rather than 1300 [nm] band is preferably used for the low cost strategy. Therefore, the restriction of light output power for safety to eyes is around single-digit stricter than that at 1300 [nm] band. Also, with regard to the lifetime, the reliability in using a semiconductor laser with this wavelength band as a light source needs to be enhanced, comparing with 1300 [nm] band. For the optical wireless communication at 850 [nm] band, since the wavelength is relatively close to the visible region, there is a disadvantage that the enhancement in minimum level of receive light is limited by the interference of white light.
Also, in the transmitter for multi-channel optical link, the restriction of light output power on safety is calculated based on the sum of the light output powers of respective channels and the radiation angle. Therefore the output-power restriction per one channel is nearly the reciprocal of the number of channels, comparing with a single-core optical transmitter. On the other hand, in the receiver, there is a problem that, due to the electrical crosstalk between channels, the minimum level of receive light becomes very difficult to improve.
Accordingly, it is an object of the invention to provide an optical transmission system that the restriction for the output power of transmit light and the restriction for the minimum level of receive light can be overcome to enlarge the transmitter-receiver allowable loss and to enhance the transmission speed and transmission distance
According to the invention, provided is a binary optical transmission system for transmitting and receiving a target transmit data to be transmitted as a binary optical transmit data composed of luminous part and non-luminous part wherein the target transmit data is transmitted and received by a coding to use a transmission code that the ratio of time of luminous part to time of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the target transmit data is less than 1.
According to another aspect of the invention, provided is a binary optical transmission system for transmitting and receiving an arbitrary bit sequence as a binary optical transmit data composed of luminous part and non-luminous part, wherein the bit sequence is transmitted by a coding that converts the bit sequence into a bit sequence that the ratio of bit number of luminous part to bit number of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the bit sequence is less than 1.
According to another aspect of the invention, provided is a binary optical transmission system for transmitting and receiving a target transmit data to be transmitted as a binary optical transmit data composed of luminous part and non-luminous part through each of multiple transmit-receive channels composing a multi-channel optical data link, wherein the target transmit data is transmitted and received by a coding to use a transmission code that the ratio of the sum of time of luminous part at each of the multiple transmit-receive channels to the sum of time of non-luminous part at each of the multiple transmit-receive channels in a time section longer than one cycle of a transmission clock used to transmit the target transmit data at each of the multiple transmit-receive channels is less than 1.
According to another aspect of the invention, provided is a binary optical transmission system for transmitting and receiving an arbitrary bit sequence as a binary optical transmit data composed of luminous part and non-luminous part through each of multiple transmit-receive channels composing a multi-channel optical data link, wherein the bit sequence is transmitted by a coding that converts the bit sequence into a bit sequence that the ratio of the sum of bit number of luminous part to the sum of bit number of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the bit sequence at each of the multiple transmit-receive channels is less than 1.
According to another aspect of the invention, a binary optical transmission system for transmitting and receiving a target transmit data to be transmitted as a binary optical transmit data composed of luminous part and non-luminous part, comprises:
a transmission unit for transmitting the target transmit data by a coding to use a transmission code that the ratio of time of luminous part to time of non-luminous part in a time section longer than one cycle of a synchronous clock for the target transmit data is less than 1; and
a reception unit composed of means for detecting a nearly intermediate value between the peak value and the bottom value of a waveform of binary data waveform, and means for determining the logic level of the binary data using the detected intermediate value.
According to another aspect of the invention, a binary optical transmission system for transmitting and receiving an arbitrary bit sequence as a binary optical transmit data composed of luminous part and non-luminous part, comprises:
a transmission unit for transmitting the bit sequence by a coding to convert the bit sequence into a bit sequence that the ratio of bit number of luminous part to bit number of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the bit sequence is less than 1; and
a reception unit composed of means for detecting a nearly intermediate value between the peak value and the bottom value of a waveform of binary data, and means for determining the logic level of the binary data using the detected intermediate value.
According to another aspect of the invention, a binary optical transmission system for transmitting and receiving a target transmit data to be transmitted as a binary optical transmit data composed of luminous part and non-luminous part through each of multiple transmit-receive channels composing a multi-channel optical data link comprises:
a transmission unit for transmitting the target transmit data by a coding to use a transmission code that the ratio of the sum of time of luminous part to the sum of time of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the target transmit data at each of the multiple transmit-receive channels is less than 1; and
a reception unit composed of means for detecting a nearly intermediate value between the peak value and the bottom value of a waveform of binary data, and means for determining the logic level of the binary data using the detected intermediate value.
According to another aspect of the invention, a binary optical transmission system for transmitting and receiving an arbitrary bit sequence as a binary optical transmit data composed of luminous part and non-luminous part through each of multiple transmit-receive channels composing a multi-channel optical data link, comprises:
a transmission unit for transmitting the bit sequence by a coding to convert the bit sequence into a bit sequence that the ratio of the sum of bit number of luminous part to the sum of bit number of non-luminous part in a time section longer than one cycle of a transmission clock used to transmit the bit sequence at each of the multiple transmit-receive channels is less than 1; and
a reception unit composed of means for detecting a nearly intermediate value between the peak value and the bottom value of a waveform of binary data, and means for determining the logic level of the binary data using the detected intermediate value.
In brief, in this invention conducted is the coding that the ratio of bit number of luminous part to bit number of non-luminous part in a time section sufficiently longer than the clock cycle is less than 1 or the coding that the ratio of the sum of bit number of luminous part to the sum of bit number of non-luminous part in a time section sufficiently longer than the clock cycle is less than 1. Then, for the reception of original signal under such coding, the powers of luminous part and non-luminous part in the receive pulse sequence are detected and the logic levels are determined whether to be xe2x80x981xe2x80x99 or xe2x80x980xe2x80x99 by using the detected values. By operating thus, the restriction for the output power of transmit light by safety and the lifetime and consumed power of light-emitting element, and the restriction for the minimum level of receive light by the interference of extraneous white light or electrical crosstalk can be overcome, therefore the transmitter-receiver allowable loss can be enlarged.